1. Field of the Invention
The present invention relates to a preform as a basis of a composite material, such as aluminum-based composite material (MMC), and a production method therefor.
2. Description of Related Art
For the purpose of dispersing a reinforcement agent (herein after referred to as a reinforcement) throughout a composite material uniformly and so on, in a conventional art, a preform of a predetermined shape is produced, and it is impregnated with melted metal of a matrix-type metal by way of a forging method and an infiltration method, so as to produce a billet.
As a production method for the above-mentioned preform, a wet method is commonly used as shown in FIG. 4. Namely, water, reinforcement (ceramic fiber) and binder are prepared, and after being mixed together and adjusted, the mixture is processed by press-forming. Next, after being removed from the press, the press-formed product is dried so as to form the preform.
The wet method mentioned above, however, has problems in that the number of processes is large, and therefore the time for production is long. Further, the preform is easily broken (has high fragility), for instance, when it is removed from the die, or during the drying and baking processes. Furthermore, since water is required for the wet method, if a process for impregnating the preform with a melted metal is located close to the process for producing the preform, there must be provided means for avoiding contact between the melting metal and the water, and therefore, the wet method comprises obstacles for industrially performing the production processes from the preform to the billet on an in-line process.
Moreover, with the wet method, metal powder, which is added for obtaining a composite material of high strength and high functionality, is oxidized. As a result, it is sometimes impossible to obtain satisfactory results.
Further, according to Japanese Laid-open Patent No. Hei 5-255776 (1993) and Japanese Laid-open Patent No. Hei 6-192765 (1994), etc., there has been proposed a dry method.
In this dry method, ceramic reinforcement and inorganic binder mainly containing SiO.sub.2 are mixed together, and after being formed by applying pressure, the mixture is heated.
Further, a dry method using an organic binder has been disclosed in Japanese Laid-open Patent No. Hei 8-53724 (1996).
In this dry method, in particular in a case where the organic binder is used, the mixture must be heated to a high temperature (600.degree. C. to 1,100.degree. C.) after being formed by the application of pressure thereto. Further, in the conventional dry method using organic binders, it is necessary to add a large amount of binder into the reinforcement. These are all problems